Sino-U.S. exchanges on climate issues will boost global negotiations in the long run, but are unlikely to facilitate a substantial climate change deal at Copenhagen talks in December, say experts in the run-up to U.S. President Barack Obama's visit to China.

Climate change is expected to be one of the main topics in discussions between Obama and Chinese President Hu Jintao during Obama's Nov. 15-18 visit.

"The world' s two largest greenhouse gas (GHG) emitters will reiterate their own stances on combating global warming, which is good for long-term global talks," said Qi Ye, a Tsinghua University climate policy expert.

"But I don't think China and the U.S. will agree a deal on targets for emissions reductions during Obama's visit. Neither do I believe any deal with specific targets will come from the Copenhagen talks," Qi said.

State and government leaders from about 190 countries will attend the 15th Conference of the Parties of the United Nations Framework Convention on Climate Change (UNFCCC) from Dec. 7 to 18 in Copenhagen, Denmark. The meeting is expected to renew GHG emissions reduction targets set by the UNFCCC Kyoto Protocol, which are to expire in 2012.

The Kyoto Protocol, never ratified by United States, gives binding targets to 37 developed nations on GHG emissions. Developing countries are not obliged to accept any targets.

"China has strictly obeyed the UNFCCC and Kyoto Protocol, and has also been making huge efforts to fight global warming," Qi said.

President Hu promised at a September UN climate summit in New York that China would cut carbon dioxide emissions per unit of gross domestic product by "a notable margin" by 2020 from the 2005 level.

President Obama has said he wants to cut U.S. emissions back to 1990 levels by 2020 and 80 percent further by 2050, but the U.S. Congress has yet to pass climate legislation.

Robert Stavins, director of the Harvard Project on International Climate Agreements, said the meeting of Hu and Obama would certainly facilitate mutual understanding on climate change issues.

China and the U.S. signed a memorandum of understanding encouraging cooperation on climate change and cleaner energy in July.

But it appeared that U.S. Congress was unlikely to complete climate legislation by the time of Copenhagen, due to great political challenges in the midst of a recession with high unemployment and other domestic priorities, Stavins told Xinhua in an e-mail interview.

"There have been dramatic changes in the political climate for climate change policy in the U.S. since President Obama took office. The timing, however, is difficult for Copenhagen," Stavins said.

U.S. top negotiator Jonathan Pershing said in October that it would be difficult to pledge an emissions target without legislation by Congress.

With commitments from the world's largest economy far from certain and other key issues unresolved after two years of talks, a new pact to combat global warming is a forlorn hope for Copenhagen, experts say.

The last negotiating session before the Copenhagen conference concluded Nov. 6 in Barcelona, Spain.

UNFCCC executive secretary Yvo de Boer said there that little progress had been made on developed countries' targets for mid-term emissions reduction and financing for developing countries to limit their emissions growth and adapt to climate change effects.

Back in 2007, the UNFCCC outlined four aspects of coordinated efforts:climate change mitigation, adaptation, financing and technology support. The 2007 declaration in Bali, Indonesia, was set to propose a "road map" for forging a new treaty in Copenhagen.

"It takes time to agree a new treaty. At least all countries will fully express their willingness to make efforts in December. First it has to be certain that the Copenhagen talks won't collapse," Qi said.